Event.observe(window, 'load', function(){

  var button = new Element('input', {type:'button',id:'add-teacher-button'});

  $('something').insert({bottom:button});//Where the button should go

  button.observe('click', function(e){
    e.stop();
    var td = new Element('td');
    td.update('text');
    var tr = new Element('tr');
    tr.insert({bottom:td});
    $('foo').insert({
      bottom: tr
    });
  });

});